The present invention relates to an aircraft wing with a wing tip device and strut extending between the wing and the wing tip device, an aircraft incorporating such a wing, and to methods of modifying an aircraft wing to install a wing tip device.
In recent years, it has become increasingly desirable to install wing tip devices to aircraft wings. It is known to install wing tip devices onto aircraft that are already in use (for example a wing tip device may be added during a major maintenance overhaul of the aircraft). This is commonly referred to as “retro-fitting” the wing tip device. It is also known to install wing tip devices during manufacture of a new aircraft, but where that aircraft was not originally designed to have the wing tip device installed, thereby enabling incremental improvements to existing aircraft designs. This is commonly referred to as “forward-fitting” the wing tip device.
A problem when attempting to retro-fit or forward-fit a wing tip device is that the wing (to which the tip devices is being fitted) was not originally designed to receive the wing tip device. In known retro-fit or forward-fit solutions, the wing tip device is either attached using splice plates or butt straps spanning the upper and lower surfaces of the wing/wing tip device, or by joining the wing tip device to the wing box by a series of tension bolts. In both these arrangements, it can be difficult to efficiently distribute the loads generated by the wing tip device during use. More specifically, the wing tip device loading is reacted through a small moment arm (the thickness of the wing box) and thus the loads in the wing tip are concentrated in a small area. This problem is especially acute for large wing tip devices (which are becoming increasingly popular). To cope with these high loads, some structural re-enforcement is often necessary. This can add weight and/or complexity to the process of retro-fitting or forward-fitting the wing tip device. Furthermore, the scope for modifying the structure of the wing is often very limited, so the structural reinforcements are often sub-optimal, compared to if they had been able to be incorporated into the wing during the initial design process.
A solution proposed to combat the problem of high loads at the wing/wing tip joint is described in US2012/112005. This describes an arrangement in which the wing tip device has two mounting formations spaced apart in a spanwise direction for attaching to the spar and/or rib of the wing. The spacing between the formations is greater than the thickness of the wing box. Such an arrangement therefore enables the bending moment from the wing tip device to be reacted over a large moment arm, and the loads to therefore be reduced. However, this arrangement is not really suitable for a retro-fit or a forward fit application, because the structural modifications to the wing are too significant.
The present invention seeks to overcome or mitigate at least some of the above-mentioned problems.